1. Field of the Invention
The present invention relates generally to heat exchangers for automotive vehicles. More particularly, the present invention relates to a method of manufacturing a manifold for an automotive heat exchanger.
2. Disclosure Information
A heat exchanger includes cylindrical manifolds (or headers) which introduce a cooling medium into the heat exchanger tubes and discharge it after it has circulated throughout the heat exchanger. Typically, the cylindrical manifolds are made by rolling a brazing sheet into a cylinder. The brazing sheet is made of a core sheet coated with a brazing substance on one or both surfaces. The manifold, the tubes and other components, such as fins, are brazed to one another by vacuum brazing or with the use of a brazing flux.
One method of making manifolds for heat exchangers includes the step of rolling the brazing sheet until both of its ends are abutted. The abutted ends are electronically welded to form a seamed pipe. A specific number of holes or slots are formed in the manifold for insertion of the tubes thereinto.
To make the holes, a punching pressure has been applied to the manifold, but under the pressure the manifolds are in danger of crushing or deforming because of the relatively weak welded seams. To avoid such problems, the holes or slots were made by a milling. The milling unavoidably produced flashes, so that the tramming of flash was required. This is a time- and a labor-consuming work. In order to keep the manifolds tough, the holes must be off the welded seam. This requires determining whether the spot to be punched for the hole is off the welded seam.
One method which overcame the problems associated with this process is disclosed in U.S. Pat. No. 4,945,635. The '635 patent teaches a method of making a header pipe (manifold) which includes the steps of preparing a core brazing sheet with a brazing substance on at least one surface. The method further includes forming a bulged portion of a semi-circular cross-section in the central section of the brazing sheet, providing apertures in the bulged portion for insertion of the ends of the tubes, and rolling the brazing sheet into a cylinder with its opposite ends being butt joined to each other. The process of the '635 patent has the benefit that by forming the apertures in the bulged portion, the header pipe is not crushed during the assembly process. However, the process requires that after the apertures are formed in the bulge portion, the brazing sheet is rolled into a cylinder with its opposite ends being butt joined to each other. It has been found that this rolling process often does not create a good overlapped butt joint between the ends of the cylinder, resulting in a gap between the ends and leakage of the header pipe.
Therefore, it would be advantageous to provide a process for making a manifold for a heat exchanger which overcomes the disadvantages associated with the prior art and which provides a leak-free seam therein.
Accordingly, it is an object of the present invention to provide a process for producing a heat exchanger manifold which produces a leak-free seam along the length of the manifold and which prevents crush or deformation during the aperture forming process.